Health officials say that as of Wednesday, 26 people in five states have been sickened by an outbreak of a rare and deadly form of meningitis. All have received steroid injections mostly for back pain. Four people have died, and more cases are expected. Here are some of the facts health officials know so far.

Q: How might people have been exposed?

A: Everyone who has become ill received an injectable steroid, methylprednisolone acetate, in their backs. It’s usually given to treat pain.

Something associated with that injection was contaminated with a fungus or a group of fungi.

The prime suspect is the steroid itself. But investigators are also looking at the anesthetic and the antiseptic that were used during the procedures, and they have been cautious not to jump to conclusions about the source.

Q: What states?

A: Florida, Maryland, North Carolina, Tennessee and Virginia.

Q: How many may have been exposed?

A: Health officials are not giving a national number.

In Tennessee, officials said on Tuesday that it was around 900 people. But that number will have grown because health officials have expanded the timeframe and number of clinics they are looking at. They did not have an updated number on Wednesday.

Q: What about the steroids?

A: So far the pharmacy has recalled three lots of the steroid that is the suspected source of the infection.

Health officials have not said how many vials comprise those three lots, but the Saint Thomas Outpatient Neurosurgery Center, which is associated with 17 of the 26 confirmed cases, received 2,000 vials of the medication. State health officials said that was the largest number of any clinic in the United States.

Q: What is fungal meningitis?

A: Meningitis is an inflammation of the lining of the brain and spinal cord. It is usually caused by a bacteria or virus, but in this case health officials believe a fungus is responsible. In one person they were able to isolate the Aspergillus fungus. That is a common fungus found in leaf mold, but Aspergillus meningitis is extremely rare.

Q: Is it contagious?

A: No, it does not spread from person to person — unlike bacterial and viral meningitis, which do.

Q: What are some of the symptoms?

A: Symptoms include worsening and severe headache, nausea, dizziness and fever.

Health officials say some of the patients in Tennessee also experienced slurred speech, and difficulty walking and urinating